In the automotive engineering sector, serial interfaces such as serial peripheral interfaces (SPI) may be used in control units for transmitting data between logic units which may be designed as integrated circuits (IC), for example. An SPI interface describes a bidirectional, synchronous, serial data transmission between a unit designed as a master and various units designed as slaves. An interface includes at least three lines between the master and a slave, generally two data lines and one clock line. For multiple slaves, each of these units requires an additional select line from the master. The SPI interface allows the setup of a daisy chain or bus topology.
In some cases, the SPI interface is not suited for transmitting time-critical control signals in order to meet real-time requirements of present security-critical applications. Frequently, only diagnostic and status information is exchanged using an SPI. Time-critical control signals are generally transmitted with a high level of complexity to the control units of the actuators and/or from the evaluation circuits of the sensors, utilizing timer units and/or proprietary interfaces.
In the use of the SPI interface in the form of a bus topology, increasingly impaired signal integrity and a high level of interfering influences result at higher data rates due to poor EMC properties. In addition, only the transmission signal is synchronously transmitted with the clock signal, whereas the phase-synchronous transmission of the reception signal becomes increasingly difficult due to the internal delay times in the slave at high data rates. Thus, when the SPI interface is used in a daisy chain topology, i.e., in a ring topology, very high latencies may result, for which reason a communication system of this type cannot be efficiently utilized in automotive control units.
A so-called three-way handshake method is used in the related art, based on a physical transmission layer such as an SPI for loss-free data transmission between two entities. During the transport of messages, the participating entities require the option of ensuring that the entity which they have contacted has received the message. A transmitting entity would thus desire an acknowledgment response when the message has arrived. Thus, a first user sends a message to a second user. Based on a ring topology, the transmitting first user, for example the master, may now read back its sent message and determine by comparison whether a transmission error has occurred; however, the first user cannot make a distinction between whether the original message has arrived at the second user with distortion already present, or whether the message arrived correctly at the second user and has been distorted on the return path. In addition, the second user, for example the slave, must be sure that its message, for example the acknowledgment, has been correctly transmitted to the first user in order to subsequently be able to occupy the memory space with new data, for example.